Capacity enlargement and downsizing of a hard disk drive have progressed with improvement in performance of its head and improvement in performance of its drive media (magnetic body).
In terms of the improvement in performance of the media drive, the capacity enlargement has progressed by increasing the surface recording density. The increase in the recording density has an issue of magnetic field expansion from a magnetic head. The issue leads to downsizing of the magnetic head, but there is a limit to such downsizing. The magnetic field expansion cannot be reduced to a certain value or below, and therefore a phenomenon called side write occurs. Side write causes writing to an adjacent track at the time of recording, which overwrites and erases previously recorded data. The magnetic field expansion also causes reading of an extra signal from an adjacent track at the time of regeneration, which causes crosstalk.
To solve such an issue, a technique such as a discrete track medium and a bit pattern medium has been developed in which a space between tracks is filled with a nonmagnetic material to separate the tracks physically and magnetically (Patent Document 1).
A coating forming composition containing a nonmagnetic material covers a magnetic layer that is formed on a substrate and has projections and recesses, and the coating is etched back by means of dry etching to the surface of the magnetic layer. Thus, the filler of the nonmagnetic material between the tracks forms a flattened surface where the magnetic layer and the nonmagnetic layer are flush. This nonmagnetic layer is in contact with the magnetic layer via its bottom part and/or side part, and therefore the magnetic material might migrate from the magnetic layer to the nonmagnetic layer. To prevent such migration, a polysiloxane-based material is used (Patent Document 2).
On the other hand, a styrene-based polymer having a photocuring portion is disclosed (Patent Document 3).